226 ORDINARY BRASSES = 1-1-5 amp. ; voltage = 4-5 ; duration, 30-40 minutes. During the whole course of the electrolysis, the liquid should be kept faintly acid. 4. Determination of the Nickel.—In presence of nickel, the nickel and zinc are determined under the conditions indicated for the electrolytic analysis of argentan. 5. Determination of the Phosphorus.—See Analysis of Phosphor Bronzes. 6. Determination of the Arsenic, Sulphur and Bismuth.—The methods given for the analysis of copper (q.v.) are followed. B. Gravimetric Methods In a small covered beaker, 0-5 gram of the sample is dissolved in 10- 15 c.c. of nitric acid (D 1-2) at a gentle heat. 1. Determination of the Tin.—When the action is complete, the solution is diluted with 15-20 c.c. of water and, if it appears turbid owing to the presence of metastannic acid, evaporated to dryness. The residue is heated for some time with a few drops of nitric acid and a little water and the metastannic acid filtered off, washed with hot water acidified with nitric acid, ignited and weighed : Sn02 X 07881 = Sn. 2. Determination of the Lead.—The liquid freed from the metastannic acid, or the original solution if the alloy does not contain tin, is treated with 3-4 c.c. of concentrated sulphuric acid, evaporated to dryness and heated on a sand-bath until white fumes of sulphuric acid appear. When cool, the residue is taken up in 50 c.c. of water, gently heated and stirred to dissolve the basic copper and zinc sulphates, allowed to cool and mixed with 15 c.c. of 95% alcohol. After standing for 1-2 hours, the lead sulphate separated is collected on a Gooch crucible, washed first with a mixture of 60 c.c. of water, 10 c.c. of alcohol and 0-5 c.c. of sulphuric acid and then with alcohol until the filtrate is neutral; the crucible is then dried in an air-oven in a roomy porcelain crucible : PbS04 X 0-6831 = Pb. 3. Determination of the Copper.—The filtrate from the lead sulphate is evaporated until the alcohol is completely expelled, the residue being heated to boiling with 100 c.c. of water and the copper precipitated with hydrogen sulphide. The liquid is decanted on to a filter and the precipitate washed first with saturated hydrogen sulphide solution containing about 20 c.c. of 2N-sulphuric acid in 100 c.c. and afterwards with saturated hydrogen sulphide solution alone ; the precipitate is dried and the copper determined as cuprous sulphide : Cu2S X 0-7986 = Cu. 4. Determination of the Iron.—The filtrate is freed from hydrogen sulphide, concentrated to a small volume, treated with a few drops of hydrogen peroxide to oxidise the iron, boiled and rendered alkaline with dilute ammonia. After a short rest on the water-bath, the precipitated ferric hydroxide is filtered, washed, ignited and weighed : Fe203 X 0-6994 = Fe. If the amount of ferric hydroxide is considerable, the precipitation should be repeated to get rid of traces of zinc. 5. Determination of the Zinc.—The liquid free from iron is neutralisedlack spots difficult to remove.